United States
          Environmental Protection
The technical organizations that contributed to the
development  of  the  hydraulic  hybrid  yard
hostler are:   U.S. EPA, ARM Terminals, Parker-
Hannifin, Kalmar Industries, FEV, Inc., R. H. Sheppard
Co., Inc., and Webasto.


Using innovative series hydraulic hybrid technology,
EPA and its industry partners have created a highly
efficient and cost-effective hybrid.  This  system is
projected to improve the stop-and-go fuel efficiency
of off-road container tractors known as yard hostlers
by 50-60 percent and reduce climate change C02
greenhouse gas emissions by over 30 percent. The
unique energy recovery technology used to stop a
hydraulic hybrid vehicle also reduces brake wear  by
up to 75 percent, increasing the net operating sav-
ings substantially.

  Each high efficiency yard hostler could
  save  a terminal operator over 1,000
  gallons of fuel per year.

Even more remarkable, when manufactured in high
volume there is the potential to recoup the hybridi-
zation costs from fuel and maintenance  savings in
three to five years.

  The lifetime fuel savings for this
  vehicle's typical 12 year lifespan could
  be over $35,000 (assuming fuel costs of
This innovative technology is simple.  The main compo-
nents in a full series hydraulic hybrid vehicle are:
• High  pressure  accumulator  — stores energy by
  using hydraulic fluid to compress nitrogen gas much as
  a battery is used to store energy in a  hybrid electric
• Rear  drive pump/motor (acting as a motor) —
  converts pressurized hydraulic fluid into  rotating power
  for the wheels.
• Low pressure reservoir —holds the  spent fluid after
  it has been used by the rear drive pump/motor.
• Rear  drive pump/motor (acting as a pump) —
  captures braking  energy by pumping  hydraulic fluid
  back into the high pressure accumulator.
• Engine pump/motor (acting as a pump) — creates
  additional high pressure fluid needed to drive the vehi-
  cle, storing any excess in the high pressure accumulator.
• Hybrid controller  — monitors the driver's accelera-
  tion and braking, and sends operating commands to
  the various hybrid system components.
A typical yard hostler vehicle used to move containers at a sea port terminal.
Hydraulic hybrid vehicles rely on proven tech-
nology which is being evaluated  in package
delivery vehicles, shuttle buses,  and  refuse
                High Pressure
                \ (Vertically
  The three key design features that contribute to im-
  proving the fuel efficiency of hydraulic hybrid vehicles
    Regenerative Braking —  To slow or stop the
    vehicle, the rotating energy of the wheels is used to
    pump fluid from the low pressure reservoir into the
    high pressure accumulator.  This stored energy is
    then used to accelerate the  vehicle.  Up to 70 per-
    cent of the energy normally wasted during  braking
    is recovered and reused.
  2. Engine Shutoff (Me reduction) — Over 40 per-
    cent of a yard hostler's working hours are spent
    waiting at the port with the engine idling. The vehi-
    cle's engine-off power steering and heating systems
    allow the engine to be shut off during these waiting
    periods.  The unique series  hybrid design also en-
    ables  the engine to be automatically  turned off
    when  it is  not  needed, such as during braking.
    These features reduce vehicle emissions, as well as
    operating and maintenance costs.
  3. Optimum Engine Control  — In the full series
    hybrid design, there is no conventional transmission
    and driveshaft to connect the engine dirctly to the
    wheels. This frees the engine to be operated at its
    best efficiency "sweet" spot,  achieving optimum
    vehicle fuel economy.